Conventionally, the mixing using a plate count method is carried out for measuring the number of microorganisms existing in food or others. Specifically, after introducing a specified amount of sample solution into a sterilized petri dish, an agar culture medium is poured into the petri dish. The agar culture medium is beforehand steam-sterilized under high pressure and retained at about 45.degree. C. Immediately after being poured into the petri dish, the culture medium is sufficiently mixed with the sample solution. Subsequently, after the petri dish is left stationary and the culture medium completely solidifies, the culture is carried out in an incubator.
In the aforementioned conventional method, however, an autoclave or other special apparatus is required for heating, dissolving and steam-sterilizing under high pressure the agar culture medium. The petri dish, a flask for dissolving the agar culture medium and a number of other glass apparatuses are also required. Furthermore, to separate and cultivate microorganisms effectively, the sample solution has to be inoculated and mixed with the culture medium efficiently in a sterile manner and within a specified time period. For this purpose a laboratory should be installed especially for the microorganism test and a sufficiently trained technical expert should carry out the test. Therefore, it was difficult to carry out the microbiological quality test in general food processing plants.
To solve the aforementioned problem various simple culture media or simple test methods have been developed. For example, in a developed method, a specified amount of sample solution is permeated into the filter paper, which was impregnated with culture medium and was then dried (the trade name "Sankoritep" manufactured by Sun Kagaku Kabushiki Kaisha) so as to grow microorganisms. In this method, by impregnating the filter paper with the test solution, the culture medium is dissolved. The microorganisms in the test solution are nourished by the dissolved culture medium to grow.
In another developed method, the agar medium (for example, the trade name "Food Plate" manufactured by Nissui Seiyaku Kabushiki Kaisha) formed thin on the surface of a synthetic resin support member is soaked in the test solution for the culture of microorganisms. In this method, by soaking the agar medium in the sample solution once, the microorganisms in the test solution adhere to the surface of the agar medium. After the agar medium is drained, the culture is carried out.
In the method in which the filter paper impregnated with the culture medium is used, microorganisms often form unshapen colonies. Specifically, in this method, the test solution is held in the fibers of filter paper just by the phenomenon of capillary attraction. Motile microorganisms can freely move in the filter paper. Therefore, different from the agar media method in which microorganisms are firmly caught in the agar gel, microorganisms form the colonies spreaded in a wide area. It is also difficult to impregnate the entire filter paper uniformly with the sample solution. Consequently, it is difficult to exactly count the number of microorganisms because of the colonies overlapping one another on the filter paper or for other reasons.
In the method in which the thin formed agar medium is soaked in the test solution, the number of the microorganisms adhering to the surface of the agar medium does not exactly correspond to that of the microorganisms existing in the test solution. Therefore, we can just know the tendency to a large or small number of microorganisms.
Wherefore, an object of the invention is to provide an apparatus for the culture of microorganisms in which microorganisms are uniformly dispersed in the test solution and can form shapely colonies.